Gravimetric measurements at the laboratory scale have been hampered by relatively ponderous equipment and inefficient measurement speeds. There is a need for more efficient methods of monitoring and recording the mass of a number of materials in order to evaluate the properties of and/or screen and select optimum candidates for further development.
The optimization of materials for use in such applications as catalysts and adsorbents requires characterization of a large number of samples of such materials often as rapidly as possible. Analytical techniques for such characterization must be fast as well as accurate to deal with the large amount of data associated with the optimization. Parallel rather than serial measurement would facilitate rapid generation of data for such characterization. These measurements are particularly useful in the determination of properties or performance of, for example, surface properties such as surface area and pore diameter, which are indicators of potential performance in a variety of applications.
Micromachining technologies have become widely available in the past decade. Silicon micromachining in particular enables full integration of mechanical and sensing elements, offering cost effective production of small transducers with the potential of producing an array of sensors as a single integral unit.
Publication US 2002/0028456 A1 discloses a sensor array disposed on a substrate to measure various material properties of samples deposited on the substrate. Samples may be deposited on the sensor in solution or by vapor deposition. Properties, which can be measured, include temperature, heat capacity, thermal conductivity, thermal stability, dielectric constant, viscosity, density, elasticity, capacitance and magnetic properties.
WO 00/20850 teaches a multi-sensor device for gravimetric chemical measurements of gaseous or vapor-state analytes comprising a substrate and a plurality of sensors made from piezoelectric elements realized with thick-film technology on the substrate. The sensors are coated with sensitive coatings for absorbing the analytes.
U.S. Pat. No. 5,983,711 discloses a temperature-controlled gravimetric moisture analyzer comprising a sample holder attached to a weighing mechanism, a temperature sensor and a heater and controller responding to the output signal of the temperature sensor. This patent does not disclose an array of weighing devices, however.
WO 03/071241 discloses a spring scale for micro-weighing comprising a load platform suspended by at least three flexural springs in a surrounding frame, with bridge-connected strain gauges for measuring strain on one side of the flexural springs. There is no suggestion of an array of weighing devices, however.
U.S. Pat. No. 4,566,326 teaches an automatic adsorption and desorption analyzer for performing measurements on a plurality of powder samples using a plurality of sample cells with associated valves, controls and sensors. The analyzer can measure surface area, total pore volume, micropore volume, average pore radius, and pore-size and surface-area distributions substantially simultaneously on a plurality of samples. This analyzer represents known art in accomplishing the purposes of the present invention.
The art does not suggest, however, either an apparatus or a method for effecting mass analyses on an array of samples contained in distinct sample holders.